Lean Idle After Hard pull

[hocka09]

Hey guys,

So as the title says I'm running really lean on idle, like 18.0-20.1, after a hard pull last night and I have no clue why. The wideband is a brand new mtx-l that I just calibrated last week so it cannot be reading wrong. Listening for exhaust leaks I cannot really hear any and the idle feels perfectly normally except for the lean a/f reading that I'm getting. I have ran about 30,000 miles on the front o2 sensor since I have owned it and who knows how many miles before that. Could it be a bad front 02? Also, the wb is in the rear o2 location (no cat), but again, I can't find any exhaust leaks. Thanks for any suggestions!

 

[hocka09]

Update: front o2 sensor is reading .05v when warmed up, not fluctuating at all

 

[GsxMan98]

I would boost leak test it you could blew a vacuum line off or intercooler pipe on the hard pull and that would explain a lean idle.

 

[hocka09]

Well it actually turned out to be one of my o2 housing bolts fell out, causing a slight leak at the downpipe. Put new ss bolts with lock washers all around and we're good to go. Thanks for your reply!

 

[hocka09]

So a few months down the road here, I've now got an lean idle issue. On a cold start my wideband will show a healthy 13.0-15.0 at idle but then once the o2 sensor stops cycling for the cold start, the a/f sinks and eventually goes below 22.4, only coming up when under load, when the car appears to be functioning appropriately. Come to a stop, however, and my wb reads 22.4 again until I get going.

I'm in the Lansing area in Michigan, and this started happening yesterday just as the weather got considerably colder. I'm sure that is just making the issues more apparent. One thing I did do was unplug the o2 to see if the car goes rich due to closed loop. While it does richen it up a little bit, the wb still reads around 17.8-18.0 at idle, dipping down into the 20's every so often. I'm going to try to visually inspect my ecu for bad caps and what not but I was hoping someone could offer me some other ideas as well.

Thanks guys.